Semi-ring light source adopts high-density LED arrangement, scientific structure design, 180° irradiation, eliminate shadow, applied to special structure installation and light direction; Multi-angle optional, suitable for different working distances; Optional diffuser plate to evenly diffuse light. Application range of character, screen printing recognition; Barcode, two-dimensional code reading; Product size measurement; Product damage and defect detection; Foreign object identification on wafer; Detection of foreign body in liquid, etc.